diff --git a/core/src/main/java/org/elasticsearch/cluster/routing/UnassignedInfo.java b/core/src/main/java/org/elasticsearch/cluster/routing/UnassignedInfo.java
index cba9acbbbb9fa..a543f4c3d3b3e 100644
--- a/core/src/main/java/org/elasticsearch/cluster/routing/UnassignedInfo.java
+++ b/core/src/main/java/org/elasticsearch/cluster/routing/UnassignedInfo.java
@@ -50,7 +50,7 @@ public final class UnassignedInfo implements ToXContentFragment, Writeable {
     public static final FormatDateTimeFormatter DATE_TIME_FORMATTER = Joda.forPattern("dateOptionalTime");
 
     public static final Setting<TimeValue> INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING =
-        Setting.timeSetting("index.unassigned.node_left.delayed_timeout", TimeValue.timeValueMinutes(1), Property.Dynamic,
+        Setting.positiveTimeSetting("index.unassigned.node_left.delayed_timeout", TimeValue.timeValueMinutes(1), Property.Dynamic,
             Property.IndexScope);
     /**
      * Reason why the shard is in unassigned state.
diff --git a/docs/reference/migration/migrate_7_0/indices.asciidoc b/docs/reference/migration/migrate_7_0/indices.asciidoc
index eeecacc06fc06..2decc6c9cdd02 100644
--- a/docs/reference/migration/migrate_7_0/indices.asciidoc
+++ b/docs/reference/migration/migrate_7_0/indices.asciidoc
@@ -5,3 +5,8 @@
 
 Due to cross-cluster search using `:` to separate a cluster and index name,
 index names may no longer contain `:`.
+
+==== `index.unassigned.node_left.delayed_timeout` may no longer be negative
+
+Negative values were interpreted as zero in earlier versions but are no
+longer accepted.